High-strength titanium base aluminumvanadium-iron alloys



United States A Patent HIGH-STRENGTH TITANIUM BASE ALUlVIlNUM- VANADIUM-IRON ALLOYS Stanley Abkowitz, Paul E. Moorhead, and James R.

Gross, Warren, Ohio, assignors to Mallory-Sharon Metals Corporation, acorporation of Delaware No Drawing. Application May 7, 1957 Serial No.657,501

7 Claims. (Cl. 75--175.5)

ductility and formability accompanied by high strength 7 in theas-annealed condition, and good ductility and extremely high strength inthe aged condition; and this application as a continuation-in-part ofthe copending application of Stanley Abkowitz and Paul E. Moorhead,filed June 19, 1956, Serial No. 592,260, now Patent No. 2,819,959.

. Furthermore, the invention relates specifically to a titanium basealloy having a minimumyield strength as annealed, of about 169,000p.s.i., with excellent elongation andbend ductility as annealed, andadequate elongation and bend ductility as aged.

Finally, the new titanium base alloy of the present invention is usefulin both the annealed and age-hardened conditions and is characterized bythe absence of compound embrittlement, good ductility and very highstrength and depth of hardening.

H Application Ser. No. 592,260 indicates that normally an increase instrength of titanium can be obtained by the addition of a strengthener.Iron may be used as' a strengthener but it is a strong compound former.

alloy without the added high oxygen content, in the as annealedcondition, and that the ultimate strength of the high oxygen contentalloy can be increased by solution treatment and age-hardening to astrength in excess of 200,000 pounds per square inch, while retainingadequate elongation and bend ductility properties.

A most important and outstanding characteristic of the alloy of thepresent invention is its high oxygen tolerance.

Another outstanding characteristic of the improved Al-V-Fe titaniumalloy described in said application Ser. No. 592,260, and also oftheimproved alloy having a high oxygen content of the present invention isthat there is no apparent embrittlement resulting from compoundformation following heat treatment or heating of any kind.

A further unusual characteristic of the improved alloy either with orwithout a high oxygen content is the ease with which it may be melted ascompared with the melting problems involved in the manufacture of amanganese-titanium binary alloy which has comparable ductility, but withwhich the problem of segregation in melting is ever present.

The improved high oxygen content alloy, as well as the same alloy with alow oxygen content, in addition to having good elongation and bendductility in the asannealed condition with a high minimum yieldstrength,

' has excellent formability. Heretofore it has been difli- Vanadium'maybe used to retard the formation of the I titanium-iron compound.However, vanadium is an expensive alloying element. Nevertheless,vanadium can be obtained at a much lower cost in the form of a masteralloy with aluminum. This creates further problems because whilealuminum like iron is a strengthener aluminum accelerates the formationof the titanium-iron compound with resulting embrittlement.

, In addition to the discovery set forth in said application Ser. No.592,260 that certain quaternary alloys of aluminum, vanadium and ironcan be made with a minimum yield strength as annealed of as high as130,000 p.s.i., and with tensile and bend ductility propertiescomparable to those in other titanium alloys now used which only have a110,000 p.s.i. minimum yield strength in the as-annealed condition; wehave further discovered that when said quaternary alloys of aluminum,vanadium and iron have a high oxygen content intentionally introducedtherein, a minimum yield strength as annealed of about 169,000 p.s.i.can be obtained while still retaining the same good elongation and bendductility properties present in the cult to obtain such a rcombinationof properties in titanium alloy material.

Furthermore, the high oxygen content alloys of the present invention arecharacterized by the discovery that thestrength level of the alloydescribed in said application Ser. No. 592,260 having an oxygen contentof 0.10%- 0.15% can be substantially increased by the intentionaladdition of oxygen to the melt or by increasing the. oxygen content ofthe sponge used until the total oxygen content of the alloy is about0.48% 0 without seriously reducing elongation and bend ductility.

The attainment of the described unusual results, characteristics andproperties in a titanium base .alloy is of outstanding importance insatisfying an existing need in the art. Prior commercial titanium alloysin which high strength approaching 200,000 p.s.i. ultimate. strengthcould be provided had little or no elongation and bend ductility in theage-hardened condition, so that such alloys could not be used where suchhigh strength was in which 'noapparent embrittlement occurs resultingfrom compound formation following heat treatment, even' required.Similarly, with prior alloys, where adequate elongation and bendductility values are present in the age-hardened condition, strengthvalues in "excess of 180,000 p.s.i. developed.

Accordingly, it is an object of the present invention to provide a newquaternary titanium sheet and bar alloy ultimate tensile strength couldnot be though the alloy contains iron and aluminum as strengtheners.

Also, it is an object of the present invention to provide a newquaternary titanium alloy which is easy to produce without segregationduring melting, Which has high strength and good elongation and bendductility and formability in the as-annealed condition and which may beage-hardened to in excess of 200,000 p.s.i. ultimate tensile strengthwhile retaining adequate elongation and bend ductility.

Furthermore, it is an object of the present invention to provide a newhigh-strength heat treatable sheet and bar titanium alloy with whichhardening to a considerable depth is possible.

In addition, it is an object of the present invention to provide a newquaternary titanium sheet alloy which is lighter in weight, or has alower density than other titanium alloys presently used which have lessfavorable properties from the standpoint of minimum yield strength, asannealed, but which other alloys may have comparable bend, tensile andductility properties.

Finally, it is an object of the present invention to provide a newquaternary titanium base sheet alloy containing about 1.5% aluminum, 8%vanadium, and 3%5% iron; and to provide a new high-oxygen contentquaternary titanium base sheet and bar alloy containing 0.8%- -1.8% A1,7.5%8.5% V, 4.5%5.5% Fe and 0.30% 0.50%

These and other objects and advantages apparent to those skilled in theart from the following description and claims may be obtained, thestated results achieved, and the described difficulties overcome by thediscoveries, principles, compositions and alloys which comprise thepresent invention, the nature of which is set forth below illustrativeof the best modes in which applicants have contemplated applying theprinciplesand which are particularly and distinctly pointed out and setforth in the appended claims forming part hereof.

The alloys of the present invention may be prepared from eithercommercial titanium or high-purity titanium. Where prepared fromcommercial titanium, a typical analysis of the material in addition totitanium, alumi num, vanadium and iron is 0.02% C, 0.01% N 0.10% 0 and0.005% H In other words, presently available sponge having a spongehardness of 120 BHN is suitable. However, since the high oxygen contentalloys of the present invention contain substantially more oxygen thanpresent in 120 BHN commercial titanium sponge, it is necessary toprovide the additional total oxygen content in the alloy either by usinga sponge having a much higher interstitial oxygen content or by addingcommercially pure T10 to the melt.

In practice, the titanium is preferably melted by the electric arcprocess in a water-cooled copper crucible either in a vacuum or in anatmosphere such as argon, and the alloying elements are added to themelt either separately or in alloying combinations of vanadium andaluminum, vanadium and iron, or vanadium, iron and aluminum, as well asTiO where a high interstitial sponge having the desired high oxygencontent is not used.

In general, the alloys of the present invention may comprise 0.8%1.8%Al, 7.5%-8.5% V, 4.5%-5.5% Fe and 0.30%0.50% 0 the balance beingtitanium. More particularly, the preferred high oxygen content alloy ofthe present invention may have a nominal composition of 1.3% A1, 8% V,Fe and 0.4% O with the balance titanium.

The alloys of the present invention after melting and casting may beprocessed in the usual manner and forged or rolled to form the desiredsemi-finished or finished product. For instance, ingots of the improvedquaternary alloys may be forged or bloomed to slab form, .hot rolled tosheet bar, and the sheet bar may be rolled to form finished sheets, say,.020" to .090 thick, say for example 0.40" sheet. Alternately, bars maybe produced by forging or blooming to billets and hot rolling the barsto the desired size, for example, bars.

Several examples of alloys disclosed in said application Ser. No.592,260 without a high oxygen content but otherwise comprising theimproved Al-V-Fe quaternary alloy of the present invention are asfollows:

TABLE I Nominal or Intended Composition Example No. Heat N 0.

Percent;

Percent Percent Percent V Fe Al Ti 8 Bal. DM 455 8 3 1.5 5 1.5 Bel.

The mechanical properties of annealed sheet fabricated from alloys inTable I as determined by evaluation, are indicated in Table II below:

tility with a minimum as-annealed yield strength of 122,200 p.s.i. andhigher with larger amounts of iron, and with freedom from embrittlementresulting from compound formation following heating or heat treatment.

These alloys likewise have a relatively low density of about 0.169 poundper cubic inch for the alloy of Example 2 which compares favorably witha higher 0.172 density for the 8% binary manganese alloy which has alower minimum yield strength in the as-annealed condition and which ismore diflicult to make because of the segregation problem in melting.

These sheet alloys of Tables I and II accordingly provide quaternarytitanium alloys which are relatively easy to make, which may have a130,000 p.s.i. minimum yield strength or higher, as annealed, with goodtensile and bend ductility, which have good forming characteristics,which have relatively low density, and which have a combination of theindicated properties heretofore not obtained in any known prior titaniumalloy.

In accordance with the further discoveries of the present invention, ifincreasing amounts of oxygen are added to the alloys of Tables I and Hthe higher oxygen content alloys are characterized by a number ofimproved properties.

Thus, a high oxygen content alloy having a nominal composition of 1.3%Al--8% V5% Fe and 0.4% 0 has the typical properties set forth in TablesHI through VII below:

MECHANICAL PROPERTIES .In 2 inches.) 2 In 1. inch.)

TABLE IV Typical room temperature properties 0) heat treated .040" sheetbar Comparing the values in Table III with those in Table 11, thepresence of 0.4% 0 in the alloy of Table III does not produce anydetrimental eifects on the elongation and bend ductility of'the alloy insheet form or on the elongation and reduction of area ductility of thealloy in bar form. However, the improved high oxygen content alloy hashigh strength and exceptionally good ductility in the annealed condition(178,000 p.s.i. U.T.S., 18.3% elongation in bar, and 178,000 p.s.i.U.T.S. and 12.9% elongation with a 2.2-4.2 T minimum bend radius insheet) in spite of the high oxygen. The high oxygen alloy also has veryhigh strength and good ductility in the age-hardened condition (195,000p.s.i. U.T.S., 190,000 p.s.i., 0.2% olfset Y.S., 12% elongation and 30.1RA in bar and 206,000 p.s.i. U.T.S. 195,000 p.s.i., 0.2% offset Y.S.,5.8% elongation and 6.1-5.9 T bend radius in sheet).

Examination of the creep properties of the improved h gh oxygen contentalloy indicates that the material may beqused safely up to 700 F.without encountering a large amount of permanent deformation.

Further, the improved high oxygen content alloy has satisfactory fatigueproperties in sheet form, comparable to those of annealed manganesebinary alloy sheet.

It has heretofore been believed that titanium alloys with a highinterstitial content have been subject to notch embrittlement, that is,the notched to unnotched ratio may be 1 and below. We have discovered,however, that the high oxygen content alloy of the present invention hasvery satisfactory properties in this respect as shown in-- TABLE VITypical n tched and unnotched tensile properties of bar NotchedUnnotched Notched/ Condition UTS (p.s.i.) UTS (p.s.i.) Unnotched RatioAnnealed 230, 000 178, 000 1. 29 Age hardened 223, 000 195, 000 1. 14

In Table VI, the notched to unnotched ratio is above 1 in either theannealed (1.29) or age-hardened (1.14) condition, and thus the alloy isinsensitive to notch embrittlement even though it has the indicated highoxygen content.

Furthermore, the new high oxygen content alloy of the present inventionis not subject to compound embrittlement as indicated by the valuesgiven in Table VII An increase in the ultimate tensile strength andyield strength and in the minimum bend values and a decrease in theelongation values in the last two lines of Table VII would indicate thepresence of compound embrittlement. However, these values in Table VIIshow marked stability, and the absence of compound embrittlement.

Investigation of the additions of increasing amounts of oxygen from the0.08% 0 present in the alloys of Table II to the 0.4% 0 in the alloys ofTables III to VII shows that the yield strength of annealed 0.040" sheetmaterial increases with the addition of oxygen up to a total oxygencontent of about 0.4% 0 then decreases somewhat until the oxygen contentis about 0.5% and then again increases until the total oxygen content isabout 0.6% after which the material is completely brittle. The ultimatetensile strength of annealed material varies in a similar manner with anincreasing total oxygen content.

The ultimate tensile strength and yield strength of 0.040" sheetmaterial which has been age-hardened vary in a similar manner withincreasing amounts of total oxygen content, the material showing thehighest values with an oxygen content of about 0.4%.

The elongation values for 0.040" annealed sheet material remainsrelatively fixed with increasing amounts of total oxygen content up toabout 0.4% 0 and the elongation values then drop off to about 10% with0.5% 0 and about 7% with about 0.6% 0 Similarly, in' the age-hardenedmaterial the elongation values are relatively constant until a totaloxygen content of about 0.4% 0 and then drop 011 with further increasingamounts of oxygen.

Finally, the minimum bend radius values (T in 0.040" sheet in annealedcondition are relatively low until the total oxygen content of about0.5% 0 is reached, after which these values rise rapidly and a similarcurve applies to the minimum bend radius values for age-hardenedmaterial.

Consequently, a total oxygen content in the improved Al-V-Fe alloy ofabout 0.4% 0 produces the best combination of mechanical properties. Thesheet material may be formed to desired shape in annealed conditionwhere elongation (12.9%) and bend (2.2-4.2) ductility values areexcellent after which formed parts may be solution-treated andage-hardened to provide finished parts having an ultimate strength of206,000 p.s.i. and a yield strength of 195,000 p.s.i.

As indicated in the foregoing tables, the improved high oxygen contentalloy may be annealed by soaking at 1250 F., then furnace cooling to 900F. and then air cooling. Thirty minutes at temperature is a suitablesoaking time for sheet whereas one hour of temperature is satisfactoryfor bar material.

The beta transus for the 0.4% 0 Al-V-Fe alloy of the present inventionis 1525:25 F., and metallographic examination discloses a structurewhich is consistently an alpha-beta structure with relatively smallparticle size.

Age-hardening may be achieved with a maximum combination of strength andductility by using heat treat- '7 merits indicated in the tables, thatis, for 0.040" sheet, the material is solution treated for one-half hourat 1375 F. and water-quenched after which the material is aged for twohours at 1000 F. and air cooled. A similar treatment is used for barexcept that the solution treatment at 1375 F. is for one hour.

End quench data indicates that hardening to a considerable depth ispossible. This is of particular significance for bar stock, particularlywhere it is desired to use large size bars because a substantial depthof hardness (hardening of sections up to at least 2%" diameter) may beobtained. Thus, high-strength bars formed of the material may be used asstructural meinbers because of the more-than-adequate elongation andreducti'on-of-area values in the age-hardened condition.

Furthermore, the high oxygen content alloy of the present invention hasa low density of 0.168 pound per cubic inch.

It is to be understood that in the foregoing tables, where intendedcomposition is indicated, there may be some variation in actualcomposition determined by chemical analyses. Compositions usually areclose to the nominal or intended composition but may vary slightlyeither way from the intended values, depending upon the ability tocontrol the exact amount of alloying additions made.

The high oxygen content alloys of the present invention accordinglyprovide quaternary titanium alloys which are relatively easy to make,which may have a minimum yield strength as annealed of about 169,000p.s.i. with excellent elongation and bend ductility values, which havegood forming characteristics, which have relatively low density, "andwhich may be age-handened to about 200,000 p.s.i. ultimate strengthwhile still retaining satisfactory elongation and bend ductility values.

In the foregoing description, certain terms have been used for brevity,clearness and understanding, but no unnecessary limitations are to beimplied therefrom beyond the requirements of the .prior art, becausesuch terms are used for descriptive purposes herein and are intended tobe broadly construed.

Having now described the invention, the features, discoveries, andprinciples thereof, the characteristics of the new alloys, severalexamples of preferred embodiments of the new alloys, and the new anduseful results obtained; the new and useful compositions, combinations,products, discoveries and principles, and reasonable me- 8 chanicalequivalents thereof obvious to those skilled in the art are set forth inthe appended claims.

We claim:

1. A titanium base alloy c onsisting o f 0.8 l.f Al, 7.5% 8.5% V,4.5%5.5% Fe, 0.30%0.50% O and the balance titanium with incidentalimpurities.

2. A titanium base alloy consisting of 1.3% A1, 8% V, 5% Fe and 0.4% Oand the balance titanium with incidental impurities.

3. A titanium base alloy consisting of 0.8%-1.8% A1, 7.5%-8.5% V,4.5%5.5% Fe, and 0.30%0.50% '0 and the balance titanium with incidentalimpurities, and said alloy having as-annealed an elongation in excess of12% and a minimum yield strength varying from in excess of 122,200p.s.i. to 169,000 p.s.i., determined by the oxygen content within therange indicated. N I

4. A titanium ibase alloy consisting of 0.8%-1.8% Al, 7.5%-8.5% V,4.5%5.5% Fe and 0.30%0.50% Q the balance titanium with incidentalimpurities, and said alloy being free from embrittlement resulting fromcompound formation following heat treatment.

5. A titanium base alloy consisting of 0.8%1.8% Al, 7.S%8.5% V, 4.5%5.5%Fe and 0.30%0.50% O and the balance titanium with incidental impurities,and said alloy having as age-hardened following heating and water'-quenching, an ultimate tensile strength of about 200,000 psi. and 5.8%elongation in 0.040" sheet form.

6. A titanium base alloy consisting of 0.8%'-1.8% Al, 7.5%'8.5% V,4.5%5.5% Fe and 0.30%'0.50% O and the balance titanium with incidentalimpurities, and said alloy having as age-hardened following heating andwater-quenching, an ultimate tensile strength of about 200,000 p.s.i.and 12.0% elongation in A" bar form.

7.-A titanium base alloy consisting of 0.8%l.8% Al, 7.5%8.5% V, 4.5%5.5%Fe and 0.30%0.50% O and the balance titanium with incidental impurities,and said alloy having as age-hardened following heating andwater-quenching, an ultimate tensile strength of about 200,000 p.s.i.and 12.0% elongation in bar form and being hardenable to a considerabledepth of the order of sections up to at least 2%" in diameter.

References Cited in the file of this patent UNITED STATES PATENTS

1. A TITANIUM BASE ALLOY CONSISTING OF 0.8%-1.8% AL, 7.5%-8.5% V,4.5%-5.5% FE, 0.30%-0.50% 02 AND THE BALANCE TITANIUM WITH INCIDENTALIMPURITIES.